[FINAL] feat: [EXC-1676] add allowed viewers variant to canister's log visibility

spec/_attachments/ic.did

@@ -3,6 +3,7 @@ type wasm_module = blob;
 
 type log_visibility = variant {
     controllers;
+    allowed_viewers : vec principal;
     public;
 };
 

spec/index.md

@@ -2603,7 +2603,12 @@ The canister logs are *not* collected in canister methods running in non-replica
 The total size of all returned logs does not exceed 4KiB.
 If new logs are added resulting in exceeding the maximum total log size of 4KiB, the oldest logs will be removed.
 Logs persist across canister upgrades and they are deleted if the canister is reinstalled or uninstalled.
-The log visibility is defined in the `log_visibility` field of `canister_settings`: logs can be either public (visible to everyone) or only visible to the canister's controllers (by default).
+
+The log visibility is defined in the `log_visibility` field of `canister_settings`:
+
+- `controllers`: only canister's controllers can fetch logs (by default)
+- `allowed_viewers`: only provided list of principals can fetch logs, the maximum length of the list is 10
+- `public`: everyone can fetch logs
 
 A single log is a record with the following fields:
 
@@ -3242,6 +3247,7 @@ CanisterHistory = {
 }
 CanisterLogVisibility
   = Controllers
+  | AllowedViewers
   | Public
 CanisterLog = {
   idx : Nat;
@@ -5878,7 +5884,7 @@ Q.canister_id = ic_principal
 Q.method_name = 'fetch_canister_logs'
 Q.arg = candid(A)
 A.canister_id = effective_canister_id
-S[A.canister_id].canister_log_visibility = Public or Q.sender in S[A.canister_id].controllers
+S[A.canister_id].canister_log_visibility = Public or (S[A.canister_id].canister_log_visibility = AllowedViewers Principals and Q.sender in Principals) or Q.sender in S[A.canister_id].controllers
 
 ```